In general, a brake system is used to decelerate, stop, or park a moving vehicle.
Among brake systems, an electronic wedge brake system (EWB), which uses an electronically controlled motor as a power source in order to generate a braking force, generates a braking force without using hydraulic pressure. Therefore, the electronic wedge brake system has a simpler structure as compared to a hydraulic pressure brake. Further, the electronic wedge brake system comes into the spotlight as a brake system that can optimally implement various electronic devices and an integrated chassis.
For example, during the braking, self-energizing of a wedge assembly operated by an actuator is performed in the electronic wedge brake (EWB). That is, a wedge is moved due to the drive of the actuator and presses the pad, and a frictional force between the pad and the disk serves as an additional input force. Due to the above-mentioned wedge operation, it is possible to obtain a large braking force for the performance of the motor.
In addition, the EWB can implement various additional functions, such as a function for maintaining a set clearance of a pad, a Fail-Safe function for suppressing a brake failure to prevent a vehicle from being abnormally rotated during normal driving, and an EPB (Electric Parking Brake) function.
The present applicant has filed several applications about the above-mentioned EWB to the Korean Intellectual Property Office. For example, the following brake system has been disclosed in Korean Patent Application No. 10-2007-0065114. The brake system implements a main braking function with power generated by one motor. Further, the brake system implements various additional functions, such as a function for maintaining a set clearance of a pad, a Fail-Safe function, and an EPB (electronic parking brake) function, by using a NSL (Non-Self Locking) screw and a solenoid mechanism interlocked with a main braking motor.
However, if one motor and a solenoid are used as described above, the solenoid should support an axial reaction force transmitted from a pad against a disk pressing force. That is, when a main braking or an additional function is performed, the solenoid is controlled so as to correspond to various regions to which an axial reaction force is applied. For this reason, a high-performance solenoid, which can sufficiently support various axial reaction forces, should be used, which causes manufacturing cost to increase.
Further, if a low-performance solenoid is used to reduce manufacturing cost, the structure is modified so as to disperse an axial reaction force by using additional members for supporting an axial reaction force transmitted from a pad, for example, an NSL (Non-Self Locking) screw to which an axial reaction force is applied and a housing in which a solenoid for fixing the NSL screw is received. In this way, it is possible to reduce a load charged by the solenoid. However, there are problems in that the design of the brake system is changed and the size of the brake system is increased.